Electric discharge apparatus



July 12, 1932. B: THOMPSON 1,867,390

ELECTRIC. DISCHARGE APPARATUS Filed Aug. 2, 1928 m ..m .PO n oh m 1o fi v A B Patented July 12, 1932 UNITED} STA ES PATENT were];

. Bao'wm. El. memsomr scnnnncmnv, NEW. xi-63K, hssreixionro eEiinuAi. finne- TRIG COMPANY, A CORPORATION or new YORK ELnciRIo nrscminen Ariehnnrirs Application filed lingu st 2, 1912's,. Serial mean.

The present invention relates to electric discharge apparatus and more partlcularlyto thermionic devices which employ electrode 2 construction subject to vibration.

Inseveral of the well-known types (if thermionic devices employed as amplifiers, de-

tectors, oscillators and the like, the source of electrons usually-takes the form of a filament suspended between rigid u supports. The length 'ofthe filament is such that when cold,

it is fairly taut andcentrally disposed ofth e electrode unit but under operating conditions, this member elongates andthenorma-l tension gives way to slack, When the '-tubeis.oper-' ating and is subjected to jarsor shock, the bowed filament-tends toinove or sway slightly toward the nearest electrode with the result that the operating characteristics of the device are impaired and considerable noise produced in theloud-speaker load. I have disby producing a particularly efiective rubbing orfrictional contact 'of the compressional "sort at this point. In order to maintainthe centrally aligned position of the expanded filament, thus further reducingthearnplitude ofvibration, I may employ in connection with thedisk, a flexible support which may serve "as an energy supply conductor. In addition to the filament,'=the remaining electrodes I are also susceptible to vibration or jarirr the event that they are suspended in the envelopebetween wires'of a pliabl'enatureor-su'pported solely fro'm one end, adding their microphoni'c effect to thatoi the filament. [-However, the order ofmagnitude'of the filament "vibration'al energy is ordinarily so;much =greater thanthat of the other; el'ectrodes that the'latfter, tho sometimes appreciable, nevertheless normally is considered negligible. 'I'qhave foundthat the disk not only serves the purreducing means in enlarged VleW-Of the attachment which forms pose ofdarnping out the vibrations of the fila- 'nient but in addition rigidly main h positionof the various which it contacts.

Among the objects of the present invention is to provide a simple and e'iiective device other electrodes with whichi s readily adaptable :to 'standard tor-ms of receiver tu'bes'and whichwill serve to dissipate the vibrational energy of the filament, 1

alsothat of remainin electrodes; more general object isto maintain the relative positions of the active members thereby to form a rigid electrode nnit;

Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 shows in perspective a screened-grid type' o'f amplifier so-c'a'lled with the improved vibrationp' ce, while Fig. '25s an the subject matter of the present invent-ion. 'Referrmg to Fig. 1, numeral 'l' ill-ustrates ianyevacuated glass envelope containing ap'lu- 'rality of electrodes shown in concentric arrangernent and including the usual *a Xial-ly issupplied with currentserially thru a horizontally disposed --fiexijb'le conductor 3 Land uprightsupport 4 which is connected to one ot-the external contact p'lugs in the base; The

lower end of :the filament is attached preferab'ly to a stout wire secured in the' press, which wire serves as the other leading in conductor. It will be evident that under operating conditions the hair-like wiref3 will "takeup substantially all-the longitudinal expansion of the filament *2 atfthe same ti'rne maintaining the latter generally .in the ani- =ally: alignedposition. The controlgridimernher is of the ordinary spiral or helical form and is supported at :the top :from .the {glass anchorirod 5'byi'nieanszof awvire-having averrtical portionvdand aihorizontal plartgtheigrid :lead "being "attached to the vflatter and taken out itlIlI'Ollgh the :top of :the envelope in" the welle'understood :nianner. The anode oomaligned rectilinear filament 2. The filament prises a hollow 'metal' cylinderand.is-gpositioned within the envelope by means :of :two

- diametrically 'opp'osed rods which are :affix'ed *the press one iof the .rods may be extended through the'bottom of the envelope to serve as a leading-in conductor. In order to intercept the electrostatic lines of force extending between the grid and anode wire is led through the stem to one of the external contacts. The screen members are supported from the stem in a vertical position by a pair of wires'10, 10, secured to opposite'sides of each memberyonly'the wire nearest the observer on the outer screen being shown infull. The outermost cylinder 8 is preferably open at the bottom but closed at .the top by means of a thin metal washer 11 in order to increase the electrostatic shielding efl'ect. The tube as described up to this point -constitutes thestandardiorm of shielded or screened-grid amplifier so-called, disclosed 7 wire spacing. 'The'number of slots correthere'are four, one eachfor the filament and and claimed in Patent No. 1,7 48,026, granted February. 18, 19,30, toLoris E. Mitchell. I

7. It is evident that in the electrode construction as shown, there is considerable tendency for the upstanding filament, and the various other electrodes, particularly the grid, and their conductors,'to vibrate or move in lateral directions, which movements under operatvingcondition's, may cause variable tube char acteristics, Imicrophonic and, other disturb-- ances.' The effect of these vibrations is accentuated inthe case ofthe filament because of its relatively small'inertia andby reason ofithe fact that it is rigidly supported only at the bottom, the upper end being flexibly mounted to allow for thermalexpansion as stated hereinbefore. In accordance with the present invention, I provide a simple and 'eflt'ective device for rigidly maintainingthe relative positions of the upper end of the various electrodes and their supports. The device takes the form of an insulating plate member or washer 12 preferably of relatively thin sheet mica and shaped in such manner as to encompassleither the'upper ends of the electrodes of their projecting lead wires. In the case of the" screened-grid type of tube shown, I prefer to fashion the vibration-reducing means roughly into. a semi-circular form with rectangular notches, slots or apertures positioned along the diameter at distances corresponding to the electrode or-lead spond to the number of projecting leads or electrode supports it is desired to encompass and in the specific embodiment illustrated,

the control grid lead and two for the uprights which are" welded to convolutions' of the in- 'nerscreen-grid 8 at diametrically opposite points. The dimensions of these slots, with v cooperating i electrodes including a the exception of that of the filament, are such as to provide a snug fit for the encompassed member. While the sides of the filament slot contact lightly with member 2, the depth preferably is considerably greater and extends well beyond the position of, the filament in order not to place an initial, strain on the latter in a direction normal to the line of the slots. The construction of member 12 may be simplified and the placing into position expedited by cutting the mica strip off to a length as will readily clear the outer I screen-gridsupports. It is apparent that the attachment may be quickly inserted into position and is simple to manufacture, also effectively spaces the various electrodes or lead wires at the proper distances apart with the result that the lateral movements of each member are precluded,particularly inadirection along the linesof the slots, hence, microphonic'disturbances are substantially avoided. The frictional contact exercised .at the sides of the filament slot does not interfere insubstantial degree with the increase. in

length of the heated member due to thermal, expansion; moreover, by applying themessure substantially equally from opposite directions, there is :no tendency to place a lateral strain or mechanical bias on the filament.

The bearing orcontact surface on the various 1* electrodes and conductors is no greater than a heavy line in width because of the thinness of member 12; this narrowness ofcontact precludes-any distortion or bending of the enveloped wire. In the event that there are no horizontally disposed leading-in conductors or supports at the upper portion of the tube, it may be feasible to utilize a circular or other symmetrical form of mica washer with holes drilled along the diametral line thru whichv the vertical wires'may be threaded. The filament aperture obviously would take the form of a slot of elongated length and having width just suflicient to accommodate the filament. While I have described the mica washer as positioned at the upper end of the electrode-structure, it will be evident that it may beplaced in other portions of the structure, for example, at the lower end or in the middle of the filament if there be excessive vibration at this place. It is also to be understood that the'vibration-reducing ex pedient is adaptable toall typesof electrode arrangements provided there is present a convenientsurface upon which the member ma be supported or may bear. V v r 5 What I;claim as new and desire to secure by Letters Patentof-the United States, is:

1. In thermionic apparatus, a plurality of filamentary source "of electrons, saidelectrodes terminating in parallellyextending conductors which are subject to vibration, and means comprising'a' strip, of insulating'material which individually embraces the extremity of each of said conductors for damping out vibrations in the respective conductors.

2. In thermionic apparatus, a plurality of cooperating electrodes including a fila ment, and a common means for reducing the vibration of each of said electrodes including the filament, said means comprising a sheet of insulating material presented edgewise to the electrodes and contacting individually with the same.

3. In thermionic apparatus, a plurality of cooperating electrodes including a filamentary cathode, and means for preventing microphonic movement of the filament, said means comprising a flat disk presented edgewise to an extremity of the filament, said member being cut away so as to provide a frictional contact with a substantial part of the periphery of said filament. v

In witness whereof, I have hereunto set my hand this 1st day ofAugust, 1928.

BROWDER J. THOMPSON. 

